The advent of smaller, more fuel efficient cars has resulted in smaller engines which must provide the power demands of the vehicle. Small engines must maintain pressure for operating power steering controls etc., and maintain operating pressure at varying altitudes as the ambient pressure decreases. Thus, an inexpensive, easily constructed pressure differential switch which will actuate other devices in sequential stages or steps as the intake manifold pressure decreases, is needed. The pressure responsive switch will sense a failure or inadequacy of manifold vacuum pressure and transduce the changing differential of pressure into electrical outputs which will first actuate an auxilary vacuum pump and then second, actuate a warning light. Prior art vacuum switches are characterized by switches which contain a large number of parts and require many steps of assembly, thereby resulting in higher costs for manufacturing such switches. U.S. Pat. No. 2,899,516 entitled, "VACUUM OPERATED SWITCH," issued Aug. 11, 1959, describes a vacuum switch connected to the intake manifold of an automobile engine so that when the car stalls out in heavy traffic, the resulting failure of intake manifold pressure will cause the switch to actuate a starting circuit and automatically restart the engine when the gear shift lever is put into neutral. This vacuum operated switch requires a large number of parts for assembly and a corresponding high manufacturing cost because of the complexity of the switch. U.S. Pat. No. 3,746,810 entitled, "PRESSURE OPERATED ELECTRIC SWITCHES WITH FLEXIBLE HELICAL BRIDGING CONTACT," issued July 17, 1973, describes a pressure operated switch which must overcome opposing biasing forces and when a reduction in pressure occurs, the switch engages terminals in two steps. Again, this switch construction requires a multiplicity of parts and assembly steps leading to a corresponding higher production cost. Therefore, it is desired to produce an economically manufactured pressure differential switch comprising a minimum number of components and associated assembly steps.